There are many circumstances, especially in the printing of continuous paper webs or sheets, where it is desirable to provide a plurality of ink jet devices each with one or more nozzles for spraying ink onto a surface (e.g. a stationary or moving paper web or sheet) to print indicia thereon. Such systems confront a number of different practical problems especially where mounted in a multi-level array.
For ink jet heads in a multi-level array, typically with a plurality of ink jet heads at each level, it is difficult to properly and effectively deliver ink to the heads so that all of the heads are provided with a substantially uniform and appropriate supply of ink. Also, typically the heads in the arrays are fixedly mounted to the supporting bars or other structures to ensure that each ink jet head remains in position during printing. This fixed mounting has been considered necessary because there is vibration of the equipment that includes the ink jet heads, either internally created in the equipment or from surrounding machinery. However when an ink jet head wears out or becomes defective it is typically necessary to shut down the entire production line while the array is disassembled and the individual ink jet head is removed. Removal of the defective head thus slows down production and increases the costs of operation. If the defective ink jet head is not removed then the array print quality may be adversely affected leading to discarding some or more of the run.
According to the present invention various systems are provided which directly confront the problems set forth above, and result in advantages and improved functionality compared to the conventional prior art systems. According to the present invention a modular ink delivery system is utilized which takes advantage of a cascading flow of ink in a plurality of containers, at least one of the containers associated with each level of the array, to properly provide the ink to the arrays, and with the necessity of only a single pump. Also the invention provides a system in which individual ink jet heads are positively guided for movement from one position to the next so that they are adjustable, and also so that they are readily removable. In fact according to one embodiment of the invention each individual ink jet head can be removed without any adverse affect whatsoever on any of the surrounding heads on any level.
According to one aspect of the present invention a modular ink delivery system for a multi-level array of ink jet heads is provided comprising the following components: A plurality of arrays of ink jet heads, at least one ink jet head provided in each array, and the arrays provided on a plurality of vertically spaced levels. A plurality of ink containing chambers, at least one for each array, positioned approximately at the level of the respective arrays, stacked one atop the other, each chamber having a top and a bottom, the bottoms of at least some chambers operatively engaging the tops of others. A connection from each chamber to the at least one ink jet head of the array associated with the chamber. And, means for automatically supplying ink to all of the chambers.
Preferably each of the chambers described above has a fluid connection between it and any chamber immediately above or below it. The means for automatically supplying ink to all of the chambers may be very simple. For example it may comprise a pump and a conduit leading from the pump to an upper of the chambers for feeding ink into a top portion of the upper of the chamber so that the ink cascades downwardly from the upper chamber to lower chambers through the fluid connections between the chambers. Each of the fluid connections may comprise a standpipe, and each chamber, except the top chamber, has a first standpipe connected to the top thereof and a second standpipe connected to the bottom thereof. The first and second standpipes are arcuately offset from each other at least about 90xc2x0, preferably about 180xc2x0.
The ink jet heads of an array are connected to a chamber associated therewith at a first vertical position. The bottom standpipe in the chamber has an open top disposed at a second vertical position higher than the first vertical position so that the chamber supplies ink to the ink jet heads connected thereto before cascading ink to a lower chamber. Each ink jet of the array may be connected to the chamber by a separate hose fitting.
A single lid may provide the bottom of a first of the chambers and the top of a second of the chambers, the lid having at least one O-ring (or like seal) associated therewith for sealing with the interior of the second chamber. The lid may be substantially permanently sealingly affixed to the interior of the first chamber. Typically the ink provided in the chambers has a viscosity of between about 1.4-2 centipoise, and a surface tension of between about 35-50 dynes per centimeter. The chamber and array at each level are preferably connected together by conduits and a vacuum degasser for de-aerating ink flowing from a chamber to an array. The vacuum degasser may be provided between the chamber and each of the ink jet heads in the array.
There may be a common support structure within which the chambers are stacked one atop the other. The common support structure may include a clamp for clamping the chambers therewithin. An ink reservoir is connected to a single pump for supplying the chamber with ink, by a first conduit, and a second conduit connected to the bottom portion of the lowermost of the stacked chambers returns ink to the reservoir by gravity flow. The clamp may be loosened and the chambers then unstacked for cleaning or replacement.
According to another aspect of the present invention, a particular mounting structure is provided for the ink jet heads that allow replacement of individual heads without necessarily having to shut down the entire line. The mounting structure is ideally utilizable with the modular, multi-level, ink delivery system described above, although it may be used in single level arrays too. When used in a multi-level array at each level a first generally horizontally extending bar is provided with first means for mounting each of the ink jet heads on the first bar so that the ink jet heads are securely held to the first bar, but are readily removably individually detached from the first bar for repair or replacement without affecting others of the ink jet heads on any level. The first mounting means may comprise: a heat sink having a top and a bottom; an ink jet head and an electrical connection element for supplying activation signals to the ink jet head mounted on top of the heat- sink; and a releasable attachment to the first bar mounted to the bottom of the heat sink. At each level a second generally horizontally extending bar may also be provided, as well as second means for mounting each of the ink jet heads on the second bar so that the ink jet heads are readily movable with respect to and guided by the second bar. The first and second bars are substantially parallel to each other and spaced from each other. The first bar may be substantially circular in cross-section and the second bar distinctly non-circular in cross-section (e.g. typically polygonal, e.g. rectangular).
According to another aspect of the present invention a modular ink jet assembly is provided comprising the following components: A plurality of ink jet heads provided in an array. A first generally horizontally extending bar. A second generally horizontally extending bar substantially parallel to the first bar. And, for each ink jet head: first mounting means for mounting the ink jet head on the first bar so that the ink jet head is securely held to the first bar but is readily movable along the first bar; second mounting means for mounting the ink jet head on the second bar so that the head is readily movable along and guided by the second bar an electrical connection element mounted by the first and second mounting means for supplying activation signals to the ink jet head.
The first and second mounting means may include a heat sink having a top and a bottom, the electrical connection element and the ink jet head mounted on top of the heat sink; and an attachment to the first and second bars mounted to the bottom of the heat sink.
Typically the second bar has first and second side edges (e.g. is polygonal or otherwise distinctly non-circular), and a bottom. The attachment to the first and second bars mounted to the bottom of the heat sink typically comprises: an arcuate bushing, having an arcuate extent of at least about 100xc2x0, for engaging the first bar; a removable clip with a channel for engaging the bottom of the second bar adjacent its first side edge; and at least one roller and cooperating support for the roller for engaging the bottom of the second bar adjacent its second side edge. The arcuate bushing preferably has an arcuate extent of 180xc2x0 or less, and the first mounting means further comprises a first screw movable with respect to the bushing into a position tightly holding the arcuate bushing in a stationary position with respect to the first bar. The first mounting means may also further comprise at least one spring pressed plunger extending from the arcuate bushing into contact with the first bar.
According to yet another aspect of the present invention a modular ink jet assembly is provided comprising the following components: A plurality of ink jet heads provided in an array. A first generally horizontally extending bar. A second generally horizontally extending bar substantially parallel to the first bar. An arcuate bushing, having an arcuate extent of at least about 100xc2x0, for engaging the first bar. A removable clip with a channel for engaging the bottom of the second bar adjacent the first side edge thereof. And at least one roller and cooperating support for the roller, for engaging the bottom of the second bar-adjacent the second side edge thereof. The details of the components preferably are as described above.
According to yet another aspect of the present invention a system is provided comprising: A plurality of ink jet heads provided in an array. A first generally horizontally extending bar. And, for each ink jet head: first mounting means for mounting the ink jet head on the first bar so that the ink jet head is securely held to the first bar but is readily movable along the first bar and individually detachable from the first bar for repair or replacement without affecting others of the ink jet heads, the first mounting means comprising an open channel-defining bushing engaging the first bar, at least one spring pressed plunger biased into engagement with the first bar in the bushing, and a first screw movable with respect to the bushing into a position tightly holding the arcuate bushing in a stationary position with respect to the first bar, and an electrical connection element mounted by the first mounting means for supplying activation signals to the ink jet head.
Oftentimes there is wayward (not properly directed) mist from the ink droplets issuing from the nozzles associated with the ink jet heads. This wayward mist can adversely affect the print quality of the web or sheet being printed. The mist may provide unwanted specs on the web or sheet being printed, and/or may build up on the ink jet devices, causing poor operation, or even precluding operation. It is for that reason that an ink mist absorbing device, such as a piece of porous metal, is interposed between a paper sheet and an ink head as seen in U.S. Pat. No. 4,628,331, or material having an affinity for ink is moved across the ink jet head adjacent the nozzle such as shown in copending application Ser. No. 08/277,075 filed Jul. 19, 1994, now U.S. Pat. No. 5,557,301. This problem may also be approached, according to the present invention, by mounting a sintered metal (of magnetic material or having a magnetic material attached) plate with respect to the front surface of an ink jet head (which has at least one nozzle for spraying ink therefrom) for absorbing wayward ink in ink mist issuing from the nozzle or rebounding from the paper or other surfaces onto which ink is directed. The mounting structure may comprise a magnet and a spring, such as a leaf spring, so that the sintered metal plate is readily releasably properly positioned with respect to the front surface and can be easily replaced.
It is a primary object of the present invention to provide for the effective ink jet printing of webs or sheets, particularly in the effect supply of ink to a multi-level array of ink jet heads, and in the proper mounting of the ink jet heads. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.